Adjustable modulator apparatus



May 311966 c. PL SMITH i i 3,249,898

ADJUSTABLE MODULATOR APPARATUS if, iig

z: f 6 uw if ff f Cf* f i V a INVENTOR.

May 3, 1966 c. l5. SMITH 3,249,898

ADJUSTABLE MODULATOR APPARATUS Original Filed Jan. l0, 1958 5 Sheets-Shea?l 2 INVENTOR. IMI/26. P J/V/f/ May 3, 1966 c. P. SMITH 3,249,898

ADJUSTABLE MODULATOR APPARATUS l `original Filed Jan. 1o, 195e 5 sheets-sheet :s

May 3, 1966 c. PjsMlTH ADJUSTABLE MODULATOR vAPPARATUS original Filed Jan. lo, 1958 5 Sheets-Sheet 5 SS L if LIN' United States Patent O M 3,249,898 ADJUSTABLE MODULATOR APPARATUS Caldwell P. Smith, Groton, Mass., assignor to the United States of America as represented by the Secretary of the Air Force Original application Jan. 10, 1958, Ser. No. 708,336, now Patent No. 3,036,268, dated May 22, 1962. Divided and this application Feb. 13, 1962, Ser. No. 173,080

3 Claims. (Cl. 332-47) The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without payment to me of any royalty thereon.

This application is a division of my application, Serial No. 708,336, filed January 10, 1958, now Patent No. 3,036,268 issued on May 22, 1962.

This invention relates to the detection, measurement, and correlation of intelligence, and particularly of intelligence which manifests itself in a series of signals (audible or visible) Whose frequency spectra establish patterns -lending themselves to electronic analysis, thereby facilitating identication of specific characteristics constituting the distinguishing attributes of the intelligence undergoing examination.

The invention has utility as a means for analysis of voice signals (speech); as a means for measuring voltage or energy distribution; as a pressure pattern analyzer; as a means of measuring the distribution of heat, or radiant energy; and in quality control and analogous operations tending to follow known probability patterns.

The invention is characterized by the provision of electronic apparatus which-when applied to speech analysis, for example-operates to compare a graduation of speech signals with a set of known coefiicients presenting a desired conguration of amplitudes constituting a reference pattern. Signals are derived from the comparison process in such manner as to produce a measurement, at each segment of the examined pattern, that is indicative of relative signal distribution only; that is, the indicated result of the pattern-matching operation is independent of signal amplitudes, per se, and reiiects only the over-all amplitude pattern, or relative distribution. Thus the systems accuracy is not impaired by sensitivity to the continuously varying amplitudes of successive speech sounds, the response being therefore .a true measure of significant speech content, in contra-distinction to mere sound. Moreover, the degree to which the system discriminates as between significant speech content, and mere sound amplitude, is controllable by simple adjustment of the design parameters.

Another important feature of the invention is the provision of means for rendering the pattern-matching system adjustable for the purpose yof discriminating on the basis of relative importance of the mate segments of the pattern: critical segments of the pattern can be made to generate a more sensitive indication of the fit than is obtainable from the non-critical segments. The relative importance of any element of the pattern can be adjusted at will. This second-order weighting -of the pattern is independent of the generalized patternmatching, and can be given any desired configuration.

Other characteristics and objects of the invention will be indicated in the following description of the invention as illustrated in the accompanying drawings wherein:

FIG. l illustrates an average pattern for the sound of the consonant s, when uttered in ordinary speech;

FIGS. 2, 4 and 7 are schematic diagrams of patternmatching correlator circuitry;

FIGS. 3 and 5 are graphs showing modulator behavior; and

at various 3,249,898 Patented May 3, 1966 ICC FIG. 6 is a graph showing a comparison of two consonant spectra.

FIG. l illustrates an average pattern for one particular consonant sound, as above noted. The word pattern,

in this context, is intended to refer to the frequency spec- K1=20 logloiei-ZO ioglolzne where:

ei=voltage measured on zth channel 2e=sum of voltages measured on all channels n=number of channels From this computation there are derived spectrum patterns that are independent of the signal amplitudes, thus permitting direct comparisons to be made, and average spectra computed.

From these considerations, in turn, there can be developed an electronic pattern-matching technique to automatically classify speech sounds, which technique uses a normalizing procedure analogous to the data computations. FIG. 2 illustrates the basic circuitry.

The voltages to be measured appear on the set of terminals e1, e2, e3, en. The pattern with which the voltages are to be compared is specied by the coeicients K1, K2, K3, Kn. These coeicients represent the pattern coordinates expressed in amplitude ratios, or in decibels, with respect to an aver-age value. Since they are with respect to an average value,

by definition. l

Referring to FlG. l, a pattern for the average (s) spectrum would be devised with a set of coeflicients equal to the amount of deviation from the Odb reference line, for each frequency channel of the analyzing filter set. For positive values of the ordinates shown in FIG. l, attenuators having attenuation in decibels equal to the value of the ordinate are required. For negative values of the ordinates of FIG. l, ampliiiers having the specied ampliiication in decibels for each frequency channel are required. Thus the set of matching coefficients or KS establish a pattern that is the invert of the spectrum norm: it is the inverted image of the normalized distribution that it is desired to matchf The weighted voltage Kie (where K1 is now expressed as an amplitude ratio) is now fed to an adding circuit. In the adding circuit the weighted channel voltage is added to the negative of the average voltage for all n channels. If the pattern matches, the `sum of these two voltages is exactly zero. If the distribution of voltages does not match the pattern specified by the Ks, the adder produces a voltage of positive or negative polarity, having magnitude proportional to the error.

The conformity of the electronic pattern-matching circuitry to the graph of FIG. l, becomes obvious. In FIG. l, the data is normalized by referring the signal in each frequency band to the average for all of the bands. The electronic circuitry proceeds in the same fashion: the summing circuit derives a voltage that is the sum of the voltages e1, e2, e3, en. A calibrated voltage divider divides the sum by n, where n is the number of channels. Thus a signal is generated that is the average ot the voltage in all of the channels, and -in each channel l fed into modulators.

vnal, as illustrated in FIG. 3.

4rnade to be equal. 'ferent elements of a pattern have different relative imerage voltage. The difference between the two signals is zero, when the distribution matches the pattern.

The output signals from the various adder circuits are The .modulators have a control signal input, and a carrier signal input, and are characterized by having an output voltage that is a maximum when the control signal amplitude is zero, and the output voltage decreases as a function of the amplitude of the control signal, being symmetrical in its characteristics, i.e.,- independent of the polarity of the control sig- The modulator may have various circuit configurations, such as using vacuum tubes, diodes, saturable reactors, and other devices as are well -known in the communications art for achieving this type 4of function, or, it may take the form of lthe diode modulator shown in this description.

The outputs from the various modulators are summed in a summing circuit to produce a signal Eeac propor- 'tional to the sum of the `output voltages from all of the modulators of the pattern. This summing circuit may take any of the various circuit coniigurations well known in the electronics art for producing the sum of a set of voltages, such as pentode tubes with a common plate resistor, triode tubes with a common cathode resistor,

f feedback amplifier summer, etc.

The summed signal Eea., provides a measure of correlation between the set of input voltages e1, e2, e3 etc. to the correlator, and the pattern represented by the coeiiicients When the distribution of voltages matches the pattern specified by the set of coeflicents, the sum signal Eem, will have its greatest amplitude, since for this condition the output from each adder circuit will be zero volts, and therefore the output from each modulator will be a maximum. This condition of pattern match is independent of the absolute amplitudes of the voltages being measured, and is only affected by their relative distribution or-pattern.

The switch S, operated by relay Ry disables the output `signal when there is no voltage input to the patternresented by e1, e2, e3, etc. are all equally important in the pattern-matching, the weightings W1, W2, W3, etc. are all However, it is often true that difportance, some elements being more critical as to exact magnitude, relative to the rest of the pattern, than others. If the elements of the distribution specified by e1, e2, e3, "etc. have varying importance, the W elements are se- Ilected so that they are graded in proportion to importance.

l The weigh-tings are achieved in either attenuator or amplifier circuits in the paths of the A.C. signals from `the various modulators p-rior to summation. If attenu- 'Aators, as implied in FIG. 2, the most important elements are assigned the least attenuation, and the attenuation is made inversely proportional to the importance weighttains several innovations. achieving the desired function. Its output is independent of the absolute amplitudes being measured, being affected only by their relative distribution. It provides an extremely tine measure of pattern-matching or correlation. It provides a means of independently adjusting the relative importance of the pattern-matching for the various elements of the pattern.

FIG. 4 illustrates the pattern-matching system in detail. This vdiagram illustrates a particular circuit configuration to achieve the pattern-matching operation illustrated in simplified form in FIG. 2. Other types of electronic devices are well known in the electronics art Ying. If amplirliers, the amplication is made proportional The pattern-matching correlator shown in FIG. 2 confor achieving the functions o-f modulators and adding.

circuits, and these can be substituted in the circuit of FIG. 4 without altering the basic function of my device, as long as the functions indicated in FIG. 2 and FIG. 3 are satisfied. The specific circuit of FIG. 4 contains additional innovations, that will be described.

Referring to FIG. 4, a set of voltages characterizing a distribution are distributed on the terminals 1, 2, 3, n, where n is the last terminal of the set. These voltages specify an unknown pattern that is to be compared with a reference pattern, in order to ascertain the degree of similarity. The voltages e1, e2, e3 etc. are D.C. voltages; however, they may represent A.C. signals, that have been rectified and liltered.

The input voltages are tapped oif in resistors Ra in order to derive their sum 2e=e1|e2r|e3l en. The summing circuit is contained in D.-C. amplifier A and feedback resistor 1R,L which comprises a conventional adding circuit well known in the electronics art. An `additional function is provided by this circuit in reversing the polarity of the 2e signal. Other adding circuits, such as pentode tubes with common plate load resistor, triode tubes with common cathode resistor, etc. such as are Well known in the electronics art, can be substituted for the circuit shown to achieve the same function. Likewise, the reversal of polarity of the 2e signal can be achieved in the summing circuit, or in a separate phasereversal circuit. The configuration of FIG. 4 achieves both of these functions.

At the output terminal of amplifier A is generated a voltage that is the negative of the sum of the voltages e1|e2|e3l en. This 'signal is connected across the tapped voltage divider R, which divides the voltage 2e in precise ratios.

The tapped voltage divider R acts as a reference element that can be used to establish the coefficients K1, K2, K3 Kn for any desired pattern'. Referring to the system shown in FIG. 2, there the pattern coefficients are Ashown connected directly to the voltage te-rminals of e1, e2, e3 etc. However, the elements establishing the pattern coeiiicients can either be in this signal path, or in the 2e path, without altering the operation of the device. This is easily seen, in the fact that the expression K :sa 161 n and 61 Iln are exactly equivalent.

FIG. 4 differs from FIG. 2, in that the pattern coeicients K1, K2, K3 have lbeen shifted to the 2e branch of the matching circuits, in order to achieve certain advantages that will be enumerated. The mode of operation is basically the same as previously described.

The tapped voltage divider R is constructed to provide a set of pattern coetiicients that are specified by the voltage ratios established by the taps. It thus provides a means of readily changing a pattern, by merely changing the taps to which connections are made.

The voltage divider shown in FIG. 4 provides a choice of thirty different possible coefficients K for each element of the pattern, spaced in equal 1 decibel incre- It represents a novel way of ments. This represents only one of many possible arrangements. Since 1 db amplitude ratios correspond to approximately a l0 percent increment-al change, the tapped voltage divider R sh-own in FIG. 4 would permit patterns to be set up in the device having a maximum amplitude ratio of 30 decibels, with each element of the pattern specified to an accuracy of percent or better. By providing suitable tapped voltage dividers, the amplitude ratio, and the number and value of the increments can be made any desired value; those specified in FIG. 4 provide `a convenient set for voice analysis, and their vvalues `are set forth in the table `appended hereto.

As an alternative to the arrangement shown, a separate voltage devider can be used for each element of the pattern, to achieve identical results.

Referring again to FIG. 4, the resistors R1 and R2 comprise the matching circuit in each channel. R1 and R2 have equal resistance, and serve to add together the voltage from a particular channel, and the weighted voltage from the Vtapped voltage divider. If the distribution el, e2, e3 etc. matches the set of coefficients K1, K2, K2 etc., these two voltages are equal in magnitude and opposite in polarity; the current flowing into point x through R1 is exactly equal to the current flowing out of point x through R2, and the potential at point x is zero. If the pattern does not matchffthe two voltages are not equal, and a dierence potential will exist at point x, causing current to flow through one of the diodes D.

The identical diodes D form one arm of an A C. voltage divider, consisting of the isolating capacitor C1 and the series resistor R3. mon to each of the matching elements. A small A.C. carriervoltage is impressed across this voltage divider circuit, thus forming a modulator.

The non-linearity of silicon, germanium, selenium, copper oxide and similar diode rectifying devices is Well known in the electronics art. In the forward, or conducting direction, these devices exhibit a resistance that decreases with increased current flow. This property is exploited in the diode modulator ofFIG. 4.

When a D.C. current flows through either diode, the resistance of the diode decreases. The magnitude of the A.C. carrier voltage appearing across the diodes is approximately R diode aoRa-i- R diode for small magnitude of E2C. Thus, .-a decrease of the diode resistance causes theoutput signal to decrease. As a result, that fraction of the A.C. carrier signal appearing across the diodes will have maximum amplitude when no D.C. current is flowing through the diodes, and will decrease in amplitude proportional to the current that flows. Thus a modulator is formed, having the general characteristic shown in FIG. 3.

Other modulator circuits having the general characteristics shown in FIG. 3 can be substituted without altering the basic function of the correlator. Thus, saturable magnetic reactors, vacuum tube circuits, and other diode circuit configurations, such as are well known in the electronics art, can be used in place of the diode modulat-ors shown. The circuit of FIG. 4 uses silicon diodes as modulators, as these are conveniently simple and compact, and when used as modulators in my circuit are extremely sensitive to small current changes.

FIG. 5 illustrates the characteristics of the silicon diodes in my modulator circuit, showing their sensitivity to very Asmall changes in control current. It also illustrates how the sensitivity of the modulator circuit can be altered at lwill, by altering the bia-s voltage on t-he diodes. This characteristic of variable sensitivity is utilized in certain features of my pattern-matching correlator that will be described.

Similar circuits are com- As indicated above, means have been provided whereby in each channel the channel voltage is compared with a reference pattern, established in terms of a set of coefficients describing a standard distribution of voltages, and the degree of matching is converted automatically to an A.C. carrier signal in each channel. The A.C. carrier signals from each modulator are added together in a summing circuit, through the coupling capacitors C2 and weighting elements W1, W2, W3 etc.

The coupling capacitors C2 serve as a low-impedance path for thev A.C. signals, -while isolating thesumming circuit for D.-C., thus'preventing interaction with the pattern-matching operation.

The elements W1, W2, W3 etc. establish the relative importance of the degree of match for each element of the pattern; the W elements may be attenuators, as shown, or amplifiers. If attenuators, the attenuation in each channel is designed to be inversely proportional to the importance of that channel. The importance weighting is independent of the general pattern-matching process. It offers very useful features in the automatic analysis of voice signals by pattern-matching, and in automatic detection.

FIG. 6 i-llust-rates some measured differences in the frequency spectra of two consonant speech sounds. The average spectra of the two sounds have a maximum difference in the frequency region between 1500 and 3000 cycles per second. Below 1500 cycles per second, the differences between the two sounds are too small and variable to be of significance in discriminating the two sounds in terms of their spectra. v

The difference plot of FIG. 6 indicates the relative importance of various frequencies in distinguishing-the two sounds. In a pattern-matching voice analyzer, discrimination of these two similar speech sounds is facilitated by providing an importance weighting, that will give greatest prominence tothose elements of the spectrum pattern that lie in the frequency range between 1500 and 3000 cycles per second.

Similarly, in analyzing the vowel sounds, the energy peaks, or formants, of thev vowel spectra, are of much greater significance than the valleys or-minima of the frequency spectra. By choosing appropriate weightings, the importance of these elements of the vowel patterns can be established, in a pattern-matching voice analyzer.

The pattern-matching system above described is independent of the amplitudes of the voltages el, e2, e3, en, being sensitive only to thepattern of their distribution. However, if the incoming distribution does not precisely match the pattern established in the machine, error voltages are developed in the various channels, proportional to the amount of error. These error voltages are also proportional to the magnitudes of el, e2 etc.

If there were no compensation for this effect, the pattern sharpness would vary with voltage amplitudes, resulting in relatively broad pattern-matching when the sum of the voltages, Ee is small, and extremely sharp pattern-matching when 2e is large.

In some applications it may be useful to have the pattern-matching sharpness vary as a function of the magnitude of 2e. In other applications, it is useful to maintain the pattern selectively constant. FIG. 4 illustrates a method of automatically compensating for changes in pattern sharpness, that Willtend to keep the pattern sharpness constant. Compensation is achieved by automatic biasing of the operating points of the diode modulators.

Referring to FIG. 5, it can be observed that the diode modulators have either sharp or broad control characteristics, depending on the amount of D.C. bias voltage that is applied. By tapping off a portion of the 2e and Ee signals in resistors R4 and R5, the diode modulators are automatically biased in proportion to the magnitude of 2e. Thus an increase in the average voltage automatically broadens the diode modulator characteristic, to compensate for the sharpening effect that would otherwise occur.

my pattern-matching elements for the automatic identication of speech sounds. A conventional set of speech analyzing filters and rectitiers are used to generate a set of D.C. signals whose distribution on the terminals T1, T2, T3 etc. are related to the speech sound at each instant. The analyzing filters and rectiiers may be of the structure shown in my U.S. Patent 2,691,137, or of the structure shown in H. W. Dudleys U.S. Patent 2,248,089 or other sets of -tilters appropriate for resolving the requency spectra of speech sounds. I

Voltages appearing on terminals T1, T2, T3 etc. are added up in a summing circuit similar to that shown in FIGS. 2 and 4 to generate a signal that is the sum of the various voltages. The polarity of this signal is reversed in a phase reversal ampiitier, and the signal is divided into precise increments on a tapped voltage divider.

A multiplicity of patterns are connected to the terminals T1, T2, etc. Each pattern is designed to co-rrespond to the average frequency spectrum for a particular, significant speech event, i.e., a speech sound, or a portion of a speech sound. These patterns are all of the type shown in FIG. 4. Thus a voice signal is automatically classified in terms of the set of patterns.

Following is a table showing values suitable for the tapped voltage divider in order to establish the indicated Weighting coethcients:

Weighting Position coefficients Voltage ratio of tap on K in decibels R +15 5. 61 5. 61 R/n +14 5. 0 2 5. 0 R/n +13 4. 46 4. 46 R/IL +12 4. 0 4. 0 R/n +11 3. 64 3. 54 Rh?l +10 3. 16 3. 16 R/n +9 2. 82 2. 82 R/n +8 2. 5 2. 5 R/n +7 2. 24 2. 24 R/n +6 2. 0 2. 0 R/n +5 1. 77 1. 77 R/n +4 1. 58 1. 58 R/n +3 1. 41 1. 41 R/n +2 1. 26 1. 26 R/n +1 1. 12 1. 12 R/n db 1.00 1. 00 R/n -1 89 89 R/n -2 795 795 R/n -3 71 71 R/nI -4 63 63 R/n -5 56 56 R/n, -6 50 50 R/n -7 447 447 R/n -8 40 40 R/n -9 355 355 R/n -10 .316 316 R/n -11 282 282 R/n -12 250 250 R/n -13 224 224 R/n, -14 200 200 R/'n -15 178 178 R/n In this table:

R=tota1 resistance of voltage divider n=number of voltages or pattern elements What I claim is:

1. In an intelligence identifying system, a modulator apparatus comprising a source of A.C. signals of small magnitude, a D.C. control current source, means' including a diode, a resistor, and a capacitor connected in Series relation to said A.C. signal source, said D.C. control current source being connected in series With said diode to provide bias voltage controlling the degree of signal modulation, a second resistor connected to said D.C. signal source, and A.C. output terminals connected across said diode, the output across sai-d A.C. output terminals being independent of the polarity of said D.C. control current vsource and said output having maximum amplitude when said D.C. current is Zero.

2. In an intelligence identifying system, a modulator apparatus comprising asource `of A.C. signals of small magnitude, a D.C. control current source, means including a pair of diodes connected inv parallel, back-to-back relationship with said A.C. source, a pair of resistance means, said D.C. control current source being connected in separate series circuits to each of said resistance means and to each of said diodes to provide bias voltage controlling the degree of signal modulation, means including a resistor and a capacitor connected in series relation to said A.C. signal source, and A.-C. output terminals connected across said diodes, the output across said terminals being independent of the polarity of said D.C. control current source, said output decreasing in amplitude with increasing amplitude of said D.C. source and said output having maximum amplitude when the amplitude of said D.C. source is Zero.

3. The apparatus as described in claim 2 which further includes means for automatically controlling the bias of each of said diodes in proportion to the magnitude of the summed signal.

References Cited bythe Examiner UNITED STATES PATENTS 2,243,527 5/ 1942 Dudley 179-1 2,446,188 8/ 1948 Miller 332-47 2,535,303 12/1950 Lewis 307-885 2,556,200 6/1951 Lesti 307-885 2,576,026 11/ 1951 Meacham.

2,666,816 1/ 1954 Hunter. 2,685,615 8/1954 Biddulph 179-1 2,755,441 7/ 1956 Gulnac .307-885 2,799,829 7/ 1957 Gordon et al. 332-47 2,875,414 2/ 1959 Wlasuk 332-52 2,911,597 11/1959 Lehman 332-52 2,964,649 12/ 1960 Vance 307-885 ROY LAKE, Primary Examiner.

ROBERT H. ROSE, ALFRED L. BRODY, Examiners.

H. W. GARNER, Assistant Examiner. 

1. IN AN INTELLIGENCE IDENTIFYING SYSTEM, A MODULATOR APPARATUS COMPRISING A SOURCE OF A.-C. SIGNALS OF SMALL MAGNITUDE, A D.-C. CONTROL CURRENT SOURCE, MEANS INCLUDING A DIODE, A RESISTOR, AND A CAPACITOR CONNECTED IN SERIES RELATION TO SAID A.-C. SIGNAL SOURCE, SAID D.-C. CONTROL CURRENT SOURCE BEING CONNECTED IN SERIES WITH SAID DIODE TO PROVIDE BIAS VOLTAGE CONTROLLING THE DEGREE OF SIGNAL MODULATION, A SECOND RESISTOR CONNECTED TO SAID D.-C. SIGNAL SOURCE, AND A.-C. OUTPUT TERMINALS CONNECTED ACROSS SAID DIODE, THE OUTPUT ACROSS SAID A.-C. OUTPUT TERMINALS BEING INDEPENDENT OF THE POLARITY OF SAID D.-C. CONTROL CURRENT 